Stabilizer with upright end tanks

ABSTRACT

A TANK FOR STABILIZING A SHIP AGAINST ROLL, THE TANK COMPRISING A MAIN BODY PORTION WITH A PAIR OF COMMUNICATING UPRIGHT END TANKS APPENDED THERETO. THE STABILIZING TANK IS PARTIALLY FILLED WITH A LIQUID SO THAT THE SURFACE OF THE LIQUID, WHEN THE TANK IS LEVEL, LIES BELOW THE TOP OF THE CENTRAL REGION OF THE TANK.

Sept. 21, 1971 F. v. A. PANGALILA ErAL STABILIZER WITH UPRIGHT END TANKS Filed May 28, 1969 2 Sheets-Sheet 1 FIG 1 m /4 L-Tzzrzz-zz'zr: :z'r n rirzzrztj/ PRIOR ART \/Z PRIOR ART m FIG.3 22 32 36 38 32 36 3a 32 22 2a 34 R 26 34 l 26 l 2 "Ln 3. 'I." 28

INVENTORS FRANS V. A. PANGALlLA JOHN P. MARTIN ATTORNEYS p 21, 1971 F. v. A. PANGALILA ETA!- 3,505,351

STABILIZER WITH UPRIGHT END TANKS Filed May 28, 1969 2 Sheets-Sheet I FIG; 6 60 FIG 'I INVENTORS FRANS V. A. PANGALILA JOHN P. MARTIN KIM jaw J AT ORNEYS United States Patent O1 iice 3,606,851 Patented Sept. 21, 1971 US. Cl. 114-125 6 Claims ABSTRACT OF THE DISCLOSURE A tank for stabilizing a ship against roll, the tank comprising a main body portion with a pair of communicating upright end tanks appended thereto. The stabilizing tank is partially filled with a liquid so that the surface of the liquid, when the tank is level, lies below the top of the central region of the tank.

BACKGROUND OF THE INVENTION Presently, there is much activity in the field of ship stabilization. Many systems have been developed, and many are currently under development, for reducing the roll in ships caused by the external environment. One system which is particularly simple and which can be incorporated in presently existing ships with a minimum of ship alteration is the passive tank stabilizer.

The passive tank stabilizer, in its simplest form, is a tank, partially filled with a liquid, lying across the width of a vessel to be stabilized. In response to the roll of: the vessel, the liquid flows to and fro in the tank and, if the tank is designed properly, the liquid flow remains 90 out of phase with the roll of the vessel. Inthis manner, the liquid in the tank creates a moment which opposes the roll of the vessel and thereby tends to stabilize same.

For reasons of design, the passive tank stabilizer is often housed below a dack of the associated ship, the deck immediately above the tank often serving as a tank cover plate. The presence of this cover plate results in What may be termed tank saturation. More particularly, the presence of the cover plate defines an upper limit to the flow of tank liquid and, as a consequence, defines an upper limit to the magnitude of the eifective stabilizing moment. It is toward increasing the roll angle at which tank saturation occurs that the present invention is directed.

SUMMARY OF THE INVENTION The present invention relates to a passive tank stabilizer to be used in ships. The tank of the present invention comprises a main body region appended to which is a pair of communicating upright end tanks. Within the tank is housed an amount of liquid whose surface, when the tank is level, lies below the upper wall of the main body region.

In operation, under normal conditions, the liquid housed Within the tank flows freely to and fro, unencumbered by the upper wall of the tank. Under severe roll conditions, however, when tank saturation plagues the tanks known to the prior art, the tank of the present invention operates extremely well. The tank liquid is not constrained by the upper wall of the tank; rather, the liquid enters the upright end tanks. In this manner, more liquid appears at the end tank regions and, as a consequence, the effective center of gravity of the liquid is moved outboard with respect to the ship. Therefore, the elfective stabilizing moment is increased.

It is therefore the main object of the present invention to provide a passive tank stabilizer unhampered by the effects of tank saturation and enjoying a large effective stabilizing moment even under severe roll conditions.

-It is a more particular object of the present invention to provide a tank stabilizer having upright end tanks so that, under severe roll conditions, tank liquid is not restrained by the upper surface of the stabilizing tank.

It is a further object of the invention to provide a passive tank stabilizer with the objects noted above, which stabilizer may be readily fitted in existing ships.

=These and other objects of the invention, as well as many of the attendant advantages thereof, will be more readily apparent when reference is made to the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view, in section, of a passive tank stabilizer known to the prior art;

FIG. 2 shows the tank of FIG. 1 under severe roll conditions;

FIG. 3 is a side view, in section, of a passive tank stabilizer constructed in accordance with the present invention;

FIG. 4 shows the tank of FIG. 3 under severe roll conditions;

FIG. 5 is a perspective view of a particular embodiment of the present invention;

FIG. 6 is a top view, in section, of the stabilizer shown in FIG. 5 and taken along line 66 of FIG. 7; and

FIG. 7 is a view of the tank shown in FIG. 5 and taken along line 77 of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION With reference first to FIGS. 1 and 2, the tank saturation drawback noted above will be explained with reference to a passive tank stabilizer known to the prior art. A conventional stabilizing tank, shown to be rectangular, is indicated generally at 10. The tank 10 is defined by a bottom wall 12, an upper wall 14, a pair of end walls 16 and a pair of side walls (not shown). The tank 10 is partially filled with a liquid, the surface of which, when the tank is level, is indicated at '18. As is well known, the liquid level 18 is determined by the desired resonant frequency of the tank.

Under conditions of operation, the tank rolls with the ship, and, as a consequence, the liquid housed therein continually flows from one end wall 16 to the other. FIG. 2 shows the tank during a roll cycle, the dynamic liquid therein defining a bore indicated at 20. When the roll of the ship is severe, as shown in the figure, the bore 20 is hampered from its free flow by the upper wall 14 of the tank. As a consequence, the height of the liquid at the right hand end Wall 16 is limited and, as a result, the center of gravity is restarined against moving outboard with respect to the ship. Thus, the effective stabilizing moment generated by the tank liquid is, too, limited. This is tank saturation.

With reference now to FIGS. 3 and 4, the tank of the present invention will be described, and so too will be described the manner in which the present invention eliminates the above-noted tank saturation drawback. The tank of the present invention is shown generally at 22l and comprises a main body region defined by a bottom Wall 24, an upper wall 26, a pair of end walls 28 and a pair of side walls (not shown). The tank 22 is partially filled with a liquid, the level of which is indicated at 30. For the tank 22' to function at the same frequency as does the tank 10, it is intended that the size of the main body portion of the tank 22 be identical to the size of the tank 10, shown in FIGS. 1 and 2, and that the liquid level 30 associated with the tank 22 be identical to the liquid level 18 associated with the tank 10.

Appended to the main body portion of the tank 22, and in communication therewith, is a pair of upright end tanks 32. These end tanks 32 are defined by the end walls 28 and the side walls (not shown) of the main body portion of the tank 22. [Further defining the end tanks 32 is a pair of inner walls 34 extending upwardly from the upper wall 26. The top of each tank 32 is fitted with a top Wall 36 having an opening '58 provided therein.

With reference now to FIG. 4, indicative of tank behavior under extreme roll conditions, the operation of the tank 22 of the present invention will be described. When the tank 22 rolls with the ship, the liquid housed therein continuously flows from one end wall 28 to the other. At or near the resonant frequency of the ship, the moving liquid forms a bore 40. In contradistinction to the operation of the prior art tank shown in FIGS. 1 and 2, the liquid in the tank 22 is not absolutely restrained by the upper wall 26. Rather, the tank liquid passes into the end tanks 32 when the roll of the ship is severe. In this manner, more liquid appears at the end regions of the stabilizing tank 22 and, as a consequence, the center of gravity associated with the volume of tank liquid is more outboard than is the case in the prior art tank illustrated in FIGS. 1 and 2. Therefore, the effective stabilizing moment associated with the tank of the present invention is substantially greater than the effective stabilizing moment associated with the tanks known to the prior art.

The openings 38 in the upper walls 36 of the end tanks are provided to allow the free passage of liquid into and out of the end tanks. Without the openings, or similarly operating provisions, pressure build-up would retard the free flow of liquid in the end tanks 32.

The tank of the present invention, shown in FIGS. -3 and 4, operates as does the prior art tank, shown in FIGS. 1 and2, under normal operating conditions. In prior art tanks, operating under low roll conditions, the upper Walls of the tanks present no problems. However, when the roll of the ship becomes severe, the passive tank stabilizer of the present invention is not plagued by the problem of tank saturation as is the tank known to the prior art. Under severe operating conditions, the liquid flowing in the tank 22 communicates both with the main body region and the end tank regions of the system; therefore, the effective stabilizing moment generated by the tank of the present invention is substantially greater than would be if the upright end tanks were omitted.

With reference now to FIGS. through 7, a tank embodying the teachings of the present invention will be described in detail. The passive tank stabilizer of FIGS. 5 through 7 comprises a main body region shown generally at 50 and a pair of upright end tanks shown generally at -52. The main body region '50 is defined by a tank bottom 54, a tank top 56, a pair of tank end walls 58 and a pair of tank side walls 60. As best seen in FIGS. 5 and 6, one of the side walls 60 is broken in such a manner that the main body portion defines a C-shaped tank. More particularly, one of the walls 60 is fitted with a second set of end walls 62 and a further side wall 64.

The end walls 58 extend upwardly beyond the upper wall 56 of the main body region 50. The same is true of the side walls 60. These extensions serve, in part, to define the upright end tanks 52. The end tanks 52 are further delineated by a pair of vertical walls 66 extending upwardly from the upper wall '56 of the central body region 50. Each end tank 52 is covered by an upper wall 68 having an opening 70 provided therein.

With particular reference to FIGS. 6' and 7, it can be seen that the stabilizing tank of the present invention is provided with nozzle defining means 72. The means 72 are in the form of flat vertical plates extending from the bottom 54 to the top 56 of'the main body region 50. These flat plates are rounded at their edges so as to smoothly direct the tank liquid therearound. As is well known, the nozzle defining means 72 sen-ve to define nozzles 74 between the central region and the end regions Of the stabilizing tank, The nozzles 74 serve the wellknown function of increasing the useful frequency range of the tank.

The present invention has been described with reference to its simplest form and with reference to a particular embodiment thereof. It should be evident, however, that many alterations and modifications may be practiced Without departing from the spirit and scope of the invention. More particularly, in the field of ship stabilization, it is important that a stabilizer be designed to conform to existing ship structures. Therefore, many shapes of the main body region, many shapes of the upright end tanks and many shapes of the nozzle defining means are possible without departing from the teachings of the invention. It is the intent, therefore, that the present invention not be limited to the above but be limited only in a manner as defined in the appended claims.

What is claimed is:

1. A passive free-surface tank stabilizer for reducing roll in a ship, the stabilizer comprising: a main body region, the length of the main body region extending transverse to the length of the ship; a pair of end chambers in communication with said main body region at the extreme lengthwise ends of said main body region, said end chambers extending above said main body region; said main body region having a main tank top and a main tank bottom, said main tank top spaced from said main tank bottom by a distance whereby the main tank top is substantially above the highest liquid level to be used in said tank stabilizer; and a body of liquid partially filling said tank stabilizer, said body of liquid being of a volume less than that of said main body region so that liquid enters said end chambers only under severe conditions of roll, and of a volume wherein the frequency of liquid transfer is substantially equal to the roll frequency of the associated ship.

2. The stabilizer as recited in claim 1 wherein each end chamber is covered by an upper plate and wherein each upper plate has an opening provided therein.

3. The tank as recited in claim 1 wherein the main body region defines a C-shaped tank.

4. The stabilizing tank as recited in claim 1 and further comprising nozzle defining means for damping the flow of liquid from one end of the tank to the other.

5. The tank as defined in claim 1 wherein the tank operates so that there is a phase difference between the roll of the ship and the position of the liquid.

6. A passive free-surface stabilizing tank for reducing the roll in ships, the tank comprising: a main body region Whose length lies transverse to the length of the associated ship; said main body region having a main tank top and a main tank bottom, said main tank top spaced from said main tank bottom by a distance whereby the main tank top is substantially above the highest liquid level to be used in said tank stabilizer; a body of liquid partially filling said tank stabilizer, said body of liquid being of a volume less than that of said main body region and of a volume wherein the frequency of liquid transfer is substantially equal to the roll frequency of the associated ship; and a pair of end tanks communicating with said main body region; the main body region adapted so that the liquid housed therein flows from one end of the tank to the other in response to the roll of the associated ship and the end tanks being adapted so that liquid flows thereinto only when the roll of the ship is severe.

References Cited UNITED STATES PATENTS 3,103,198 9/1963 Ripley 114-125 FOREIGN PATENTS 1,006,036 9/1965 Great Britain 114-1Z5 TRYG-VE M. 'BLIX, Primary Examiner 

